Heat-resisting alloy



' creases until it becomes like Patented June 28, 1927.

UNITED STATES DI SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

GERALD n. nnornr,

PATENT OFFICE.

mcr-nnsrsrme A LOY.

Io Drawing.

This invention relates to heat resisting alloys and more particularly to alloys which are capable of withstanding high temperatures in air without oxidation.

Alloys having this property of withstanding high temperature are not new, since cerlain alloys of nickel and chromium which are now commonly used have this property to a high degree. These alloys. one of which is known in the trade ,as nichrome are, however, quite high in cost because of the high price of the chromium and nickel of which the alloy is almost entirely composed. The object of my invention isto produce an alloy which may be used for castings at a cost which will not be so much greater than cast iron as to render its use prohibitive.

It has been known for some time that aluminum alloyed with iron greatly improves the heat resisting qualities of the iron. If enough aluminum is added, however, to be of substantial benefit the alloy becomes too brittle for practical use. An iron-aluminum alloy containing about 10% of aluminum hasexoellent heat resisting properties but does not have the proper mechanical properties to fitit for the ordinary service to which castings may be subjected. As the percentage of aluminum is increased the brittleness of {he alloy inass.

I have found that by intro ucing into the alloy a substantial percentage of nickel, the alloy loses its brittleness without losing any of its capabilities of withstanding high temperature. -About or 40% of nickel in an iron-aluminum alloy containing from u 10% to 15% aluminum makes the alloy extremely tough. I have also found that by adding a small percentage of chromium the size of the grains in the alloy is reduced and the alloy correspondingly improved. Other metals such as molybdenum, titanium, tungsten, vanadium and uranium may be used instead of chromium for rendering the grains of the iron finer. y

The metal forming the base of the alloy may be ordinary low carbon steel or even commercial iron. A steel containing 0.02% or less of carbon, 0.04%orless of sulphur and 0.03% or less of phosphorus, 0.15% or less of silicon is satisfactory for my purpose.

Appllcation Medium 17, 1921. Serial No. 478,422.

In making the alloy it is preferable to use an electric furnace, since it lends itself more readily to the controlling of the alloy. The furnace for this purpose should pref- .alloy. Even a small percentage of silicon in the alloy would be objectionable. When the aluminum is not added in the furnace but is added in the ladle, the basic lining becomes less important.

The iron and nickel are melted in'the furnace and then tapped on to the aluminum which has been preheated to a molten condition in the ladle. Care should be taken to have the iron and nickel mixture thoroughly deoxidized before adding it to the alumi num. It is preferable to have the carbon as low as possible and in case the material used runs a little higher than approximately .01% in carbon, the carbon should be reduced in the furnace before making the alloy. This applies also to the elements phosphorus and sulphur. None of the furnace slag should be allowed to come into contact with the metal afterthe aluminum is present. The molten aluminum and the alloy after the addition of the aluminum should be kept covered with a special slag of cryolite or a cryolite lime mixture to protect the aluminum from oxidation. Cryolite is used because of its solubility for aluminum oxide. Care should be taken'to havethe metal in the furnace just hot enough to pour cleanly from the ladle but not superheated. The cooler it is when casting the better the grain obtained.

I have found that a very satisfactory alloy has the following content:

. Per cent.

Aluminum 10 Chromium 5 Nickel 30 "Iron These percentages may, of course, be va- (ill ried. For instance, the nickel may be in- I creased to 35% or even 50% and the iron correspondingly reduced; The content of the aluminum and the chromium may also be varied. In this particular alloy, the pereentage of chromium is a little larger than 1s necessary for reducing the size of the ains of the material. percentage is arge enough to. harden and toughen the i alloy When making the castings every 6 tion should be taken to prevent oxidation of the molten metal. This may be done by filling the moulds beforehand with'a non-oxidizing gas such as nitro en or carbon dioxide or by dusting the mou ds lightly, but thoroughly, with cryolite to dissolve the oxide film formed between the ladle and the mould This prevents the formation of cold shuts mechanical strength is greater than that of.

ordinary cast iron. In casting, no more care tion thereto,

is required than in the case of ordinary cast stee This application is a continuation in part of my application, Serial No. 401,650, filed August 6, 1920.

While I have d'escribed,my invention as embodied in concrete form and as operating in a specific manner in accordance-with the provisions of the patent statutes, it should be understood that I do not limit my invensince various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. An alloy which resists oxidation at precauv and from 40 to 60 percent iron.

2. An alloy which resists oxidation at high temperatures having an iron base andcontainmg 10 to 15 per cent of aluminum and a larger amount of nickel 3. An alloy which resists oxidation at high temperatures containing over 40'per cent of iron, the remainder consistin of approximately 5 per cent of chromium, a larger amount of nickel than chromium, and a substantial amount of aluminum.

4. An alloy which resists oxidation at high temperatures containing from 10 to 15% of aluminum, 5% or more of chromium,a larger amount of nickel than aluminum, and approximately of iron.

5. An alloy containing 40 to per cent of iron, the remainder consisting principally of nickel, suflicient aluminum to prevent oxi-. dation at high temperatures, and at least 5 per cent of chromium, the nickel content being greater than the aluminum and chromium contents. I

6. An alloy which resists oxidation at high temperatures having an iron base and containing from 10% to 15% aluminum and'at least 25% of nickel.

7. An alloy which resists oxidation at high temperatures having an iron base and containing from 10% to 15% of aluminum and between 25% and 40% nickel and a small percentage of chromium.

8. Analloy which resists oxidation at high temperatures having an iron base and containlng about 10% of aluminum, 30% to 40% of nickel and 5% of chromium.

In witness whereof, I have hereunto set my hand this 16th day of June, 1921.

GERALD n. BROPHY. 

